It can cause physiological and behavioral changes in infants such as pain, tachycardia, hypoxemia, increased blood pressure, grimacing, prolonged crying, and irritability. Vaccination is an important part of neonatal nursing care. Newborns express their pain nonverbally and behaviorally. Therefore, any pain assessment is based on the ability of others to recognize pain symptoms. This randomized controlled trial was planned to evaluate the effect of heart sound and white noise on pain and physiological parameters during intramuscular injection of hepatitis B vaccine in newborns. This randomized controlled study used parallel trial design.

The research hypotheses are H1: Neonates in the heart sound group will have lower procedural pain scores than neonates in the control group. H2: Neonates in the white noise group will have lower procedural pain scores than neonates in the control group. H3: Neonates in the heart sound group have lower procedural heart rate peak values than neonates in the control group. H4: Neonates in the white noise group have lower procedure-related peak heart rates than neonates in the control group. H5: Neonates in the heart sound group have higher procedural oxygen saturation values than neonates in the control group. H6: Neonates in the white noise group have higher procedural oxygen saturation values than neonates in the control group.

Methods The study was designed as a randomized controlled trial. The population of this study will consist of newborns who are followed up at Bartın Maternity and Children's Hospital. Statistical power, type I error, effect size, and study design will be taken into account when calculating the sample size. The study will be designed to have a power of at least 80% and a type I error rate of 5%. As there is no similar study evaluating the effect of heart tones and white noise on pain and physiological parameters during hepatitis B vaccination in children, the effect size of the study will be aimed at medium (0.25) to determine the sample size. Based on a medium effect size (f: 0.25), 80% (1 - β error) power and 95% (α error) confidence level, and taking into account data loss, it was calculated that the sample size should be increased by 10%, and the sample size of 33 newborns in each group should consist of 99 newborns in total G*Power 3.1.9.7.

Before starting the study, mothers will be informed about the purpose of the study and the heart sound and white noise applications to be applied and their written informed consent will be obtained. After written informed consent has been obtained from the mothers, the newborns will be randomised to 3 groups (heart sound, white noise, control group) by a statistician independent of the study (www. randomize.org) using a computer program. All newborns will receive a standardised approach. Standardised approach: All Hep B vaccine administration will be performed by a nurse during the morning shift and administered intramuscularly through the vastus lateralis muscle at a 90-degree angle using a 1-inch 23-gauge needle to infants in all three groups. All conditions such as room temperature (25°C), light, injection procedure will be the same in all three groups. Neonates will be fed at least 30 minutes before the procedure. Care will be taken to avoid non-nutritive sucking, touching or swaddling the baby during the procedure to avoid confusion with other pain relief methods. Aseptic techniques are observed during all procedures.

During the implementation of the measurement tools, the researcher will go to the relevant facility herself and the data collection forms will be applied face to face. The researcher and the nurse will not use any aromatic substances in the baby monitoring room during the study.

Inclusion Criteria:

• Gestational age of 38-41 weeks,
• Newborn birth weight >2500 g
• Stable vital signs before the procedure,
• Postanatal age between 2-28 days,
• No contraindications to the administration of hepatitis B vaccine
• Delivery of the newborn to the mother after birth
• Consent of the parents of the newborn to participate in the study
• Fasting less than 3 hours/30 minutes before feeding
• A valid score on the newborn hearing screening test
• Newborn not crying before vaccination

Exclusion Criteria:

• Newborn babies requiring respiratory support,
• Newborns with any neurological disorder (seizures)
• Newborns taking opiates or born to mothers taking opiates
• Newborns receiving muscle relaxants, sedatives, analgesics
• Babies with major congenital anomalies
• Neonates with an APGAR score of less than 7 at 5 minutes
• Neonates who have undergone surgery
• Newborns with birth trauma (especially rapid delivery)
• Conditions that may prevent communication with parents (e.g. speech problem)
• Hearing impairment
• Newborns who will be transferred to another hospital